Brazil's currency hit a new low against the dollar amid increasing concerns that the country's policy makers are failing to reinvigorate the South American economy.

The real weakened to 2.4098 to the dollar on Monday, trading above 2.4 for the first time since March 2009. The decline came on the same day the central bank held a series of auctions that injected $3.6 billion into the foreign-exchange futures market, in an attempt to...